A scan type radar apparatus that detects an object and the like may be used in a monitoring system or the like. For example, an FM-CW (Frequency Modulated-Continuous Wave) radar apparatus continuously transmits a transmission wave without intermission by periodically changing the frequency of the transmission wave. Because the frequency of the transmission wave is changed when a reflected wave from a detection target is received, a time delay of the reflected wave may be measured from a frequency difference between the transmission wave and the received reflected wave, in order to detect a distance from the FM-CW radar apparatus and the detection target and a moving velocity of the detection target. For this reason, when the FM-CW radar apparatus is used in a traffic monitoring system, for example, and a number of vehicles and a velocity of the vehicles traveling in each lane of a road are detected by the FM-CW radar apparatus, it is possible to detect a state of the traffic in each lane of the road may, and an obstructing object such as trash existing on the lane of the road.
The FM-CW radar apparatus detects the detection target by pairing a difference between the transmission wave and the reflected wave in a frequency raising interval, and a difference between the transmission wave and the reflected wave in a frequency lowering interval. For example, the detection results of a predetermined number of pairs within a certain time are output outside the FM-CW radar apparatus with a predetermined format. For this reason, when the number of pairs becomes extremely large as a result of the pairing, data of the detection target are desirably transferred at a relatively high transfer rate. However, the development time and the development cost would increase if a radar apparatus capable of transferring the data at the high transfer rate were to be developed, and it is difficult to create a relatively inexpensive radar apparatus.
On the other hand, when the transfer rate of the data of the detection target is relatively low, the number of detection targets (that is, the number of pairs) detectable within a predetermined time becomes limited. Consequently, in the case of a vehicle radar, for example, which is relatively inexpensive but has a relatively low data transfer rate, the increase in the development time and the development cost may be suppressed, however, the number of detectable detection targets becomes limited.
Examples of radar apparatuses are proposed in Japanese Laid-Open Patent Publications No. 2006-163879 and No. 2001-223660, for example.
According to the conventional radar apparatus, it is difficult to output the detection results of a relatively large number of detection targets when the data transfer rate is relatively low.